Most neurostimulators on the market were originally developed for stimulation of nerves in the spinal cord to treat chronic pain. In most cases the neurostimulators were not intended for stimulation of nerves in the neck and face. The neurostimulators can be relatively large, since they were designed to be placed in the body such as the torso and chest areas. Because of their relatively large size, when these neurostimulators have been adapted for use (off-label) by physicians to stimulate nerves in the neck or head area, they have been implanted in the chest, torso, or back of the patient and not in the head.
In addition, the typical neurostimulators that have been available deliver electrical stimulation that is a train of pulses with selected, fixed parameters such as pulsewidths, amplitudes, and stimulus frequency. Stimulus pulse amplitudes are generally a constant voltage or a constant current amplitude, but not both. Whether the neurostimulator provides constant voltage stimulus or constant current stimulus is based on the design of the neurostimulator. These typical stimulation choices are limiting and are not optimal for every treatment use.
Headache, migraine, and facial pain disorders are a substantial health concern that can have a negative impact on social activities and work. In some instances, it can lead to over consumption of pain relieving drugs. There has been some clinical work to use neurostimulators that have been designed for spinal cord stimulation to treat headache and migraine. The neurostimulator is implanted subcutaneously (under the skin) either in the chest or back area of a patient and a stimulation lead or leads, connected to the neurostimulator, are tunneled underneath the skin, up the neck, and to a target nerve such as the occipital nerve. Stimulation (usually a train of electrical stimulus pulses at a fixed frequency) is delivered from the neurostimulator and via electrode contacts located at the distal end of the stimulation lead or leads to stimulate the target occipital nerve in order to alleviate migraine or headache.
There are some drawbacks with these existing adapted neurostimulator systems. The spinal cord neurostimulators are relatively bulky and were never intended to be implanted in the head, so they must be implanted in the back, torso or chest of a patient. The leads must be tunneled through the neck into the head. Since there is a great deal of movement in the neck, there will be twisting action that causes the stimulation lead to move. It is desirable to minimize lead movement once the lead is implanted.
In addition, it has been found that the conventional, fixed stimulation frequencies, e.g., 35 Hz, offered by these neurostimulators, while adequate for conventional spinal cord stimulation, do not always provide relief from migraines or headaches. Unlike the mechanism of chronic pain that is treated with spinal cord stimulation, headaches and migraines are believed to arise from many different causes and, hence, the present inventors have surmised that a neurostimulator that can offer a wider variety of stimulation other than a fixed 35 Hz stimulation would have a greater chance to successfully treat more incidences of headaches and migraines.
Neurostimulators and stimulation leads used in spinal cord stimulation have also been adapted for use in deep brain stimulation (“DBS”). Deep brain stimulation is currently being used to treat movement disorders such as Parkinson's disease and essential tremor. A lead extension may be used to connect the neurostimulator to the stimulation lead. The lead extension or the stimulation lead is tunneled subcutaneously through the neck and to the top of the head, through a hole at the top of the skull, and into the brain. Again, the drawbacks are that the neurostimulator has to be placed in the chest, torso or back and not in the head. The stimulation lead or lead extension must be tunneled through the neck which subjects the lead or lead extension to unwanted movement.
Nevro Corporation provides a neurostimulator in their HF10™ system that is approved and marketed purely for spinal cord stimulation and which offers selectable stimulus frequencies up to 10 kHz. Stimulus amplitudes and pulsewidths, as well as frequencies appear to be fixed, once selected and programmed. The Nevro neurostimulator is sized and shaped to be placed generally in the torso back, side or front chest area, and is specifically designed to stimulate the spinal cord with multiple stimulation channels. The Nevro neurostimulator is not intended to be implanted in the head since it is too large and bulky. Although the Nevro neurostimulator offers higher frequency stimulation than conventional spinal cord stimulators, the Nevro device cannot be implanted in the head. In addition, there is no known use of a Nevro neurostimulator for stimulating nerves in the head or neck or stimulating the brain for DBS application.
It would be desirable to have neurostimulators and stimulation systems that can provide a wider choice of stimulation patterns to stimulate various nerves in the body, and in particular nerves and ganglions in the head, face and neck and also for DBS applications.